The present invention relates to a method of cleaning probes, a probing method and a prober, and more specifically, to a method of capable of cleaning probes while an object to be examined, such as a semiconductor wafer (to be abbreviated as "wafer" hereinafter) is placed on a main chuck, a probing method of the same type, and a prober.
As a typical example of a conventional prober, a prober for electrically examining semiconductor integrated circuits (to be called "IC chips" hereinafter) formed on a wafer, will now be described.
As can be seen in FIG. 6, for example, a conventional prober 10 includes a cassette C for storing wafers W, a loader unit 11 for conveying wafers W from the cassette C, a prober unit 12 for examining wafers W conveyed by a conveying mechanism (not shown) provided in the loader 11, a controller for controlling the prober unit 12 and the loader unit 11, and a display device 14 which also serves as an operation panel for operating the controller 13.
A sub-chuck (not shown) is provided for the loader unit 11. The wafers W are pre-aligned by the sub-chuck with reference to the orientation flat, and the pre-aligned wafers W are conveyed to the prober unit 12 by the conveying mechanism.
In the prober unit 12, a main chuck 15 movable in X, Y, Z and .theta. directions, on which a wafer W is placed, an alignment mechanism 16 having an alignment bridge 16A or the like, for aligning a wafer W placed on the main chuck 15 accurately at a test position, probes (e.g. probe needle) 17A for performing an electrical test on a semiconductor integrated circuit (IC chip) formed on a wafer W aligned by the alignment mechanism 16, and a probe card 17 having the probe 17A, are arranged.
A head plate 18 is made to be openable in the upper surface of the prober unit 12. The probe card 17 is fixed via an insert ring 18A to an opening made at the center of the head plate 18. On the prober unit 12, a test head 19 is placed to be revolvable. The probe 17A is electrically connected to a tester (not shown) via the test head 19 revolving on the prober unit 12. A predetermined electrical signal outputted from the tester is transmitted via the probe 17A to an IC chip formed on the wafer W placed on the main chuck 15, and via a reverse route, a signal containing the result of the measurement of the electrical properties of the IC chip is transmitted to the tester. The tester thus carries out an electronic test on each of the IC chips on the basis of such a signal.
In order to test a wafer W, the main chuck 15 is moved in the X, Y and .theta. directions by the driving mechanism, and thus the wafer W on the main chuck 15 is aligned with the probe 17A. Then, the main chuck 15 is driven upwards (in the Z direction) such that an electrode pad (made of, for example, aluminum) of the IC chip formed on the wafer W is brought into contact with the probe 17A. In this operation, if a natural oxide film (made of aluminum oxide) or the like is formed on the surface of the electrode, the electrical connection between the probe 17A and the electrode pad fails. When this happens, the probe 17A scrapes off the natural oxide film or the like formed on the electrode pad 17A, and then they are brought into contact with each other, thus assuring the electrical connection between them. After a great number of tests, a residue O of aluminum oxide scraped off from electrode pads is stuck on the probe 17A as shown in FIG. 7, and as a result, the tests thereafter cannot be performed accurately.
In order to avoid this, conventionally, the terminal of the probe 17A is cleaned. In the example shown in FIG. 8, the terminal of the probe 17A is cleaned by a grinding plate 20. The grinding plate 20 is attached on an attachment plate 15A extending from the lateral surface of the main chuck 15. The terminal of the probe 17A is brought into contact with the grinding plate 20 and as the main chuck 15 is moved up and down, the terminal of the probe 17 is ground, thus eliminating the residue O.
As another example, a device having a grinding file placed at the central portion of the main chuck, has been developed (see Japanese Utility Model KOKAI Publication No. SHOWA 59-148251).
In the case of the conventional device in which the grinding plate for grinding the probes 17A is attached onto the attachment plate 15A provided on the lateral surface of the main chuck, the probes 17A is pressed by the grinding plate, and therefore a large bending moment is applied on the main chuck 15 via the attachment table 15A. In order to withstand the bending moment, the main chuck 15 is required to have a high mechanical strength. In particular, when the size of wafer is enlarged in diameter (for example, 12 inch diameter), the size of the main chuck 15 is increased accordingly, thus further increasing the bending moment. In order to deal with such an increased bending moment, it is required not only simply enlarging the main chuck 15, but also to reinforce the mechanical strength of the main chuck 15. Thus, the weight of the main chuck 15 is further increased, which is not desirable.
The above-described conventional device, and another type of the conventional device, in which the grinding file is placed on the central portion of the main chuck entail a problem that the wafer must be unloaded from the main chuck each time the probes are subjected to cleaning.
As the size of wafers W is enlarged in diameter, the number of IC chips formed on one wafer W is remarkably increased, and therefore the number of probing carried out for one wafer W is accordingly increased. As a result, a great amount of residue 0 is stuck to the probes 17A, and therefore there is an increased necessity of cleaning the probes 17A during the series of tests. In the case of the conventional cleaning device, the following operation is necessary. That is, the testing is paused, and the wafer W is once unloaded from the main chuck to the loader chamber. Subsequently, the probes 17A are ground, and after that, the wafer is loaded back onto the main chuck. Then, the wafer W is aligned and the test is continued once again. Thus, it requires a great amount of time to test one wafer W.